Hip dysplasia is a potentially debilitating disease in dogs with a breed-related incidence reaching seventy percent or higher. Using existing methods, dogs are not determined to be free of hip dysplasia until two years of age. Recent work has demonstrated the utility of stress radiography to diagnose passive hip laxity in puppies as young as four months of age. Smith, G. K. et al., "New Concepts of Coxofemoral Joint Stability and the Development of a Clinical Stress-Radiographic Method for Quantitating Hip Joint Laxity in the Dog," JAVMA 196:59-70 (1990) and Smith, G. K. et al., "Coxofemoral Joint Laxity from Distraction Radiography and Its Contemporaneous and Prospective Correlation with Laxity, Subjective Score, and Evidence of Degenerative Joint Disease from Conventional Hip-Extended Radiography in Dogs," Am. J. Vet. Res. 54:1021-42 (1993).
Ultrasonography has been used to diagnose human hip dysplasia since the early 1980s. Initially, ultrasonography was used to describe morphological characteristics related to the coxofemoral joint components. Ultrasound techniques measure the distance traveled by the head of the femur from compression to distraction of the hip joint. Manual compression and distraction are not always adequate to diagnose hip laxity in young dogs because varying results arise from differences in techniques and strength of the clinician.
Recently, diagnostic ultrasound has also been advantageously employed to image the coxofemoral joint and to diagnose hip laxity in puppies. Ultrasonic imaging during manual compression and distraction of the coxofemoral joints of dogs placed in ventral recumbency was described by O'Brien, R. T. et al., "Ultrasound Diagnosis of Hip Dysplasia in Two Litters of Puppies," Veterinary Orthopedic Society Twentieth Annual Conference, Lake Louise, Alberta, Canada, Feb. 27-Mar. 6, 1993. A more extensive report by the same researchers was published at O'Brien, R. T., et al., "Dynamic Ultrasonographic Measurement of Passive Coxofemoral Joint Laxity in Puppies," J. Am. Anim. Hosp. Assoc. 33:275-381 (1997). A shortcoming of the O'Brien et al. method is that it, like the Smith method, requires two clinicians, one of which positions the pelvic limbs while the second obtains the images.
See also Trout, N. J. et al., A Prospective Study of Canine Hip Dysplasia Using Ultrasound: A Preliminary Report," Europ. College of Veterinary Surgeons Second Scientific Annual Meeting, Cambridge, England Jun. 2-4, 1993, Abstract No. 16 and Harcke, H. T. and L. E. Grissom, "Performing Dynamic Sonography of the Infant Hip," A Jr. 155:837-844 (October 1990) and Saies, A. D., "The Value of a New Ultrasound Stress Test in Assessment and Treatment of Clinically Detected Hip Instability," J. Ped. Ortho. 8:436-441 (1988).
Specialty instruments can assist in the hip distraction process. U.S. Pat. No. 5,482,055 (Smith) describes a method and apparatus for determining hip joint laxity in a dog. Smith describes a method for determining hip joint laxity in which radiographic images of the hip joint in compression and distraction are compared using a gauge to determine a distraction index. The dog, which can be only as young as about sixteen weeks, is placed in dorsal recumbency and the hips are manipulated as described. Smith also describes an apparatus for distracting the hips. However, the apparatus can only be used on a dog placed in dorsal recumbency and requires one clinician to manipulate the apparatus and a second clinician to obtain the radiographic images.
A method for determining coxofemoral joint laxity in puppies by a single clinician is still not known in the art. Therefore, what is desired is a method for distracting and for measuring distraction that can be accomplished by a single clinician. An apparatus suitable for use in such a method would also be desired.